This invention relates generally to the field of magnetic disc recording units. More particularly it relates to such units utilizing rigid recording discs of smaller than standard diameter to achieve a compact unit while still taking advantage of the advanced technology associated with such units of substantially larger size.
In the prior art it has been known to provide disc recording units utilizing a plurality of coaxial, rigid magnetic recording discs. Such discs conventionally were of about 14 inch diameter and were fabricated of aluminum coated with a suitable magnetizable coating. In the more advanced units utilizing the known technology the magnetic transducer heads which are used for reading and writing data on the discs are supported a fixed and relatively critical distance above the surface of the disc by the aerodynamic lift caused by the interaction of the moving air film carried by the flat surface of the rotating disc and a carefully designed transducer head configuration. Through the use of this advanced technology and the precision available through the use of fixed, instead of removable, disc recording media, it has been possible to achieve very high densities of data recorded on such discs. However, such conventional disc drives have generally been large console units, suitable only for relatively large installations because of both size and costs.
It has been conventional for applications requiring smaller size and/or lower costs in disc storage units to utilize disc drives incorporating a single flexible recording disc. Such a disc conventionally was of about eight inch diameter and was formed of a thin sheet of plastic material such as Mylar coated with a suitable magnetizable material. These disc drives conventionally could utilize only a single such disc, which is insertable and removable by the operator into and out of the disc drive. The inaccuracies associated with both the insertion and clamping of such a disc and the inaccuracies inherent in such a flexible and deformable medium have conventionally required that data tracks thereupon be spaced substantially apart, thus resulting in substantially lower recording density. Thus, the combination of mounting only a single disc at a time and the low data densities available have severely limited the usefulness of such small recording units.
Recently much effort has been made to combine the best features of both the large, sophisticated units and the small, inexpensive flexible disc drives. In such hybrid units discs generally similar to those used on large, sophisticated units, such as the Memorex Model 3650, but having a diameter of less than nine inches, and suitably about eight inches, have been provided, with a plurality of such discs on a single spindle. Also, advanced technology transducer heads have been utilized to achieve the high recording density required. In other respects, these small units were designed along conventional lines as well. For example, the conventional spacing between adjacent coaxial discs has been on the order of 0.3 inch, a spacing which has been found to yield highly satisfactory results in the larger units. However, in the development of these smaller, rigid disc drive units, a number of unexpected problems relating to the conventional technology were discovered. Apparently as a result of the substantially reduced volume of air contained within the disc drive enclosure, defined by the base plate and the housing cover, previously satisfactory air flow patterns were found to be severely disrupted. Specifically, it was found that using conventional technology resulted in highly undesirable turbulence of the air flow over certain portions of the disc surfaces, thus causing erratic spacing of the "flying" transducer heads above the disc surface and severely disrupting the desired recording and reading operations. Additionally, in view of the heat generated by the various motors for rotating the discs and for advancing and retracting the transducer heads, it became apparent that the reduced volume of air would cause undesired thermalgradients within the recording unit, particularly where external cooling fans had been eliminated to reduce the costs, size and complexity of the system. In an effort to overcome these problems one manufacturer of such disc drives has placed a specially designed shroud between adjacent discs in an effort to improve air flow. However, problems have still remained, and such shroud again adds to the complexity and cost of such a recording unit, both being undesirable characteristics.